Phosphatidylcholine (PC) serves not only as a major component of cellular membranes, but also as a major source of fatty acyl donors for triacylglycerol biosynthesis in eukaryotic organisms. At least three pathways through which PC is generated exist: (i) the CDP-choline pathway where diacylglycerol (DAG) is a direct precursor; (ii) a pathway where CDP-DAG is a direct precursor, involving phosphatidylserine formation and decarboxylation and phosphatidylethanolamine methylation (Zheng and Zou, 2001); and (iii) a pathway with LPC as substrate. The third pathway is exerted by LPC acyltransferases (LPCAT).
LPCAT enzymes catalyze the acylation of LPC molecules to form PC and play a pivotal role in membrane biogenesis. They can also exert a reversible reaction to release the fatty acyl chain esterified to the sn-2 position of PC, thereby contributing to a continuous remodeling of fatty acyl-CoA and PC pools.
The significance of LPCAT in glycerolipid metabolism of eukaryotic systems has been noted for many years. For genetic engineering of plant-based production of very long chain polyunsaturated fatty acid (PUFA), this enzyme is believed to represent a bottleneck for acyl exchange between the fatty acyl elongation and de-saturation systems. In higher plants, the function of this enzyme is largely unknown, but it has been proposed that the enzyme is involved in the selective incorporation of fatty acids into storage pool.
Although LPCAT relating to the synthesis of surfactant lipid located on the surface of (pulmonary) cells have been reported in mammalian systems (Chen X et al., PNAS 2006 103:11724-11729; Nakanishi H et al., JBC 2006 281: 20140-20147), an LPC transferase involved in membrane or storage lipid synthesis has not been reported.
Recently, a mitochondrial acyl-CoA independent LPCAT from Saccharomyces cerevisiae has been identified. This enzyme has been shown to function in cardiolipin metabolism (Testet et al. 2005). In addition, Shindou et al. (2007) reported that aceyl-CoA:lyso-PAF (platelet-activating factor) acetyltransferase possesses LPCAT activity.